Selective hydrocracking process



Dec. l, 1K964 D. A. YOUNG SELECTIVE HYDROCRACKING PROCESS Filed March26, 1962 MOA/CYCL /C 25 645 OIL FEE@ .United States Patent O 3,l59,567@ELECTIVE HYDRCRACKING PRCESS Dean Arthur Young, Yorba Linda, Calif.,assigner to Union @il Company of California, Los Angeles, Calif., acorporation of California Filed Mar. 26, T1962, Ser. No. 182,263 Claims.(Cl. 20S- 87) This invention relates to catalytic hydrocracking, andmore particularly is concerned with methods for converting highlyparaiiinic hydrocarbons in the gas oil boiling range to lower boilingparaffin hydrocarbons, boiling for example in the gasoline or jet fuelranges. More particularly, the process is concerned with new methods forincreasing the selectivity of hydrocracking, i.e., for maximizing theyield of products in the desired boiling range, while minimizing theproduction of very light hydrocarbons such as methane, ethane, propane,and the like. The process also results in a maximum'production ofhighoctane isoparaiins, as opposed to the relatively lowoctane normalparatins. Brieiiy stated, the invention comprises the essential step ofincluding with the primary paraiiinic feedstock to the hydrocrackingzone, a minor proportion of monocyclic aromatic hydrocarbons. In onespecic modification of the process, a gas oil feedstock is rstseparated, as by solvent extraction, into a paraliinic ratiinate and anaromatic extract; the lighter fraction of the aromatic extract issubjected to hydrodealkylation to produce naphthalene and a mixture oflight monocyclic aromatic hydrocarbons, and at least a portion of thismonocyclic fraction is then blended with the parainic ratlnate from thesolvent extraction, and the mixture is subjected to catalytichydrocracking.

It is known in the art that optimum hydrocracking conditions forconverting parafnic hydrocarbons differ considerably from the optimumconditions for converting aromatic hydrocarbons. It has hence beenproposed in the pastto separate hydrocracking `feedstocks into arelatively aromatic fraction and a relatively paraflinic fraction, andto subject the two fractions to separate hydrocracking under optimumconditions for each fraction. It has now been found however that theeiliciency of cracking of the parainic portion of feed can be furtherirnproved by incorporating therein a desired proportion of monocyclicaromatic hydrocarbons. It has further been found that polycyclicaromatic hydrocarbons such as naphthalene and the like are undesirablein the paraffin hydrocracking zone because they unduly repress theoverall activity of the catalyst. Monocyclic aromatics on the 'otherhand do not significantly depress the activity of the catalyst forpromoting the desired conversions, but on the contrary have a favorableiniiuence in improving the selectivity of hydrocracking, and improvingthe octane value of the gasoline produced by increasing the ratio ofiso/normal parat-'tins therein.

The inventionmay perhaps be more readily understood from theaccompanying drawing, which is a how-sheet illustrating one particularmodification thereof. The initial feedstock, consisting for example of astraight-run gas oil boiling between about 40G-800 F., is brought in vialine 2 and separated into a relatively aromatic and a relativelynon-aromatic fraction in solvent extraction column 4. Any conventionalmethod of separating aromatics from non-aromatic hydrocarbons maybeemployed, as for example aZeotr-opic distillation, selective adsorption,extrac- 3,l59,567 Patented Bec. 1, 1964 lCe tive distillation and thelike. However, inthe modification illustrated, the feedstock isintroduced into the bottom of countercurrent extraction column 4, whichis preferably packed with a suitable material such as Raschig rings orthe like to facilitate contact between countercurrently owing immiscibleliquids. The solvent employed for the extraction may comprise any of theWell known polar compounds which exhibit a selective solvency foraromatic hydrocarbons as opposed to non-aromatic hydrocarbons, and whichare suitably low-boiling. Suitable solvents include for example ethanol,methanol, phenol, furfural, ethylene glycol monomethyl ether,acetonitrile, sulfur dioxide and the like.

The solvent is admitted to the top of column 4 via line 6 and passesdownwardly, countercurrently to the risingl hydrocarbon stream. Thearomatic extract is Withdrawn at the bottom of the column via line 8,and transferred to a small fractionating column 10, from which thevolatile solvent is removed as overhead via line 12, condensed andrecycled to the top of extraction column 4. kThe stripped aromaticextract, comprising both monocyclic and polycyclic aromatichydrocarbons, is transferred via. line 13 to a second fractionatingcolumn 14, from which a light fraction boiling between about 400 and 550F. is taken overhead via line l5, while the heavier polycyclic aromaticsare withdrawn as bottoms via line 16. This bottoms fraction may ifdesired be subjected to additional hydrogenation and/ or hydrocrackingin facilities not shown.

The overhead fraction in line 15 contains higher alkylated benzenes suchas durene, di-isopropyl benzene and the like. It also contains a desiredproportion, depending upon the selected end-boiling-point of thefraction, of bicyclic aromatics such as naphthalene, methylnaphthalenes, dimethyl naphthalenes and the like. Where maximumnaphthalene production is desired from the subsequent dealkylation step,the end-boiling-point of the overhead is about G-550 F., so as toinclude most of the methyl and dimethyl 'naphthalenes in the extract,while still excluding the tricyclic hydrocarbons. Where naphthaleneproduction is not a prime consideration a lower end-point in the rangeof about 425-500 F. may be selected.

In any case, the overhead fraction in line l5 is subjected todealkylation in hydrodealkylation unit 17. Hydrodealkylation is effectedfor example by passing the overhead in admixture with steam and1,000-10,000 scf. of hydrogen per barrel, over a cobaltmolybdate-alumina catalyst containing about 1% of NaOH, at about l,050F. and 1,000 p.s.i.g. Such a dealkylation procedure is described morespecifically in U.S. Patent No. 2,734,929, and its eitect is to convertmethyl naphthalenes to naphthalene, and higher alkyl benzenes primarilyto benzene, toluene and xylenes.

The hydrocarbon product from dealkylation unit 17 is transferred vialine 18 to fractionation column 19, from which crude naphthalene isrecovered as bottoms via line 20. The overhead fraction comprisesbenzene, toluene and xylenes, and is transferred at least in part vialine 21 to line 2S for use in admixture with the parafnic raflinate ashydrocracking feedstock.

i The rainate from extraction column 4, comprising nou-aromatichydrocarbons containing a small amount of dissolved solvent, iswithdrawn via line 22 and sent to rainate stripping column 24, fromwhich -solvent is recovered overhead via line 26 and recycled to line 5for reuse in extraction column 4. The bottoms from stripping column 24is withdrawn via line 2S and mixed with monocyclic aromatics from line21 as previously described.

In the solvent extraction method illustrated, it will normally be foundthat most of the naphthenes which may have been present in the feed willbe recovered along with the paraiiins in line 28. Broadly speaking, theterm paraffin as used herein is intended to include both openchainparaflins and cyclo-paraflins. However it is also contemplated that theconditions of extraction in column 4 can be suitably adjusted, as byincreasing the solvent/oil ratio, so that a greater portion, or even themajor portion, of the naphthenes can be extracted along with thearomatic hydrocarbons, thus producing an essentially naphthene-freeraiiinate.

The mixed hydrocracking feed in line 23 is blended with recycle andfresh hydrogen from lines 30 and 32, and the mixture is then passed intohydrocracking reactor 34 via preheater 36. Hydrocracking proceeds inreactor 34 under the following general conditions:

TABLE 1 Hydrocrackz'ng Condilz'ons The eiiluent from hydrocracker 34 iswithdrawn via line 38, condensed and transferred to high pressureseparator 40 via condenser 42. Recycle hydrogen is withdrawn via line 30and recycled as previously described. The liquid condensate in separator40 is then flashed vialine 44 into low pressure separator 46, from whichlight hydrocarbon gases are exhausted via line 48, while remainingliquid condensate comprising gasoline and/or jet fuel is withdrawn vialine S0, and sent to additional fractionation facilities not shown.

It is not intended that the invention be limited to the detailsdescribed above. In particular, it is contemplated that pure or mixedmonocyclic aromatic hydrocarbons derived from extraneous sources may beemployed instead of monocyclic hydrocarbons derived from the particularfeed used. Specifically, hydrocarbons such as benzene, toluene, ortho,meta, or para-xylene, ethylbenzene, cymenes, cumene, trimethylbenzenes,tetramethylbenzenes, pentamethylbenzene, and the like may also be used.Any proportion of such aromatic hydrocarbons added to the paraftinicportion of feed will benefit the hydrocracking to some extent, but it ispreferred to use about 0.5% to by volume thereof, based on theparaliinic feed. In most cases, it is found that the monocyclic aromatichydrocarbons are relatively unaffected during the hydrocracking,although some cracking of side-chains may occur, as well as someisomerization and/ or disproportionation.

The paralilnic feedstock used in the hydrocracking step may comprise anymineral oil fraction boiling above about 350 F., and up to about 900 F.,which contains less than about 2% by volume, and preferably less thanabout 0.5 of polycyclic aromatic hydrocarbons. Where the feedstockcontains more than about 2% by volume of polycyclic aromatichydrocarbons, little or no benefit is obtained by adding monocyclicaromatics to the feed in respect to the advantages here sought, namelyimproved selectivity of hydrocracking and improved isoparaiiin/normalparaiiin ratios in the product. Feedstocks of this character can beobtained by many methods other than that illustrated. Many straight-rungas oils derived from paratiinic crude oils may be found suitable assuch, or after a minimal treatment with silica gel or activated carbonto adsorb most of the polycyclic aromatic hydrocarbons. Fractionalcrystallization may be employed in some instances to crystallize out adesired proportion of the polycyclics. Also, in some instances, theinitial solvent extraction step may be controlled, as by reducing thesolvent/oil ratio, so as to selectively extract the polycyclic aromaticswhile leaving the major portion of monocyclic aromatics in theparafiinic raiiinate.

Suitable catalysts for use in the hydrocracking step of this inventionmay comprise any desired combination of a refractory cracking base witha suitable hydrogenating component. Suitable cracking bases include forexample mixtures of two or more difiicultly reducible oxides such assilica-alumina, silica-magnesia, silica-zirconia, alumina-boria,silica-titania, silica-zirconia-titania, acid treated clays and thelike. Acidic metal phosphates such as aluminum phosphate may also beused. The preferred cracking bases comprise composites of silica andalumina containing about 50-90% silica; coprecipitated composites ofsilica, titania, and zirconia containing between 5 and of eachcomponent; partially dehydrated, zeolitic, crystallinemolecular sieves,e.g., of the X or Y crystal types, having relatively uniform porediameters of about 8 to 12 angstroms, and comprising silica, alumina andone or more exchangeable zeolitic cations. Any of these cracking basesmay be further promoted by the incorporation of acidic halides such ashydrofluoric acid, boron tritiuoride, silicon tetraiiuoride and thelike.

A particularly active and useful class of molecular sieve cracking basesare those having a relatively high SiO2/Al203 ratio, eg., between about2.5 and 6.0. The most active forms are those wherein the exchangeablezeolitic cations are hydrogen and/or a divalent metal such as magnesium,calcium or zinc. In particular, the Y molecular sieves, wherein theSiO2/Al203 ratio is about 5, are preferred, either in their hydrogenform, or a divalent metal form. Normally, such molecular sieves areprepared iirst in the sodium or potassium form, and the monovalent metalis ion-exchanged out with a divalent metal, or where the hydrogen formis desired, with an ammonium salt followed by heating to decompose thezeolitic ammonium ion and leave a hydrogen ion. It is not necessary toexchange out all of the monovalent metal; the final compositions maycontain up to about 6% by weight of Na2O, or equivalent amounts of othermonovalent metals. Molecular sieves of this nature are described moreparticularly in Belgian Patents Nos. 577,642, 598,582, 598,683 and598,682.

As in the case of the X molecular sieves, the Y sieves also containpores of relatively uniform diameter in the individual crystals. In thecase of X sieves, the pore diameters may range between about 6 and 14A., depending upon the metal ions present, and this is likewise the casein the Y sieves, although the latter usually are found to have crystalpores of about 9 to l0 A. in diameter.

The foregoing cracking bases are compounded, as by impregnation, withfrom about 0.5% to 25% (based on free metal) of a Group VIB or GroupVIII metal promoter, e.g., an oxide or sulfide of chromium, tungsten,cobalt, nickel, or the'corresponding free metals, or any combinationthereof. Alternatively, even smaller proportions, between about 0.05%and 2% of the noble metals, c g., platinum, palladium, rhodium oriridium, may be employed. The oxides and sullides of other transitionalmetals may also be used, but generally to less advantage than theforegoing.

In the case of zeolitic type cracking bases, it is desirable to depositthe hydrogenating metal thereon by ion exchange. This can beaccomplished by digesting the zeolite with an aqueous solution of asuitable compound of the desired metal, wherein the metal is present ina cationic form, and then reducing to form the free metal, as describedfor example in Belgian Patent No. 598,686.

The following example is cited to demonstrate the beneficial effect ofadded monocyclic paraflins during hydrocracking of a paraffin feed, andthe detrimental effects of polycyclic aromatics:

EXAMPLE In this example, n-decane was subjected to hydrocracking in aseries of experiments, with and without Various aromatic hydrocarbonsadded thereto. The hydrocracking catalyst was composed of 16 to 30 meshgranules of an 89% silica-11% alumina carrier, upon which wasimpregnated nickel nitrate from an aqueous solution, followed bycalcining at 1,000" F. to give 13.9 weight-percent nickel on thefinished catalyst. Prior to the runs this catalyst was pre-reduced withhydrogen for 1 hour at 800 F., presuliided with a thiophene-'heptanemixture for 4 hours at 600 F., and halided for 3 hours at 500 F. bytreatment with 5 volume-percent trifluorotoluene in heptane. f

The etfect of aromatic hydrocarbons on the hydrocracking was determinedby successively hydrocracking the following feedstocks:

n-Decane n-Decane-I-S mol-percent benzene n-Decane-j-S mol-percent mixedXylenes n-Decane-j-S mol-percent naphthalene The hydrocrackingconditions in each case were held constant at 550 F., 1,000 p.s.i.g.,1.0 LHSV, and 20,000 s.c.f. of hydrogen per barrel of feed. Thefollowing table shows the effects of the various aromatics upon thehydro'- cracking of n-decane:

TABLE 2 Run No.

5 mol 5 mol 5 mol Total aromatics in feed 0. percent percent percentbenzene xylenes naphthalene Conversions, vol. percent oi Iced:

To Cri-C product 20 17 12 0.8 To 120-335" F. product 18 18 18 7. 2Iso/normal paraiiin ratios in product:

Butaues 3. 2 2. 8 2. 5 2. 6 Pentanes 6. 5 7. 3 8. 4 (b) Hexanes 6. 7 7.6 10. 7 (b) Aromatics in feed, vol. percent:

Benzene 0. 0 2. 34 0.0 0.0 0. 0 0. 0 0. 13 0. 0 0. 0 0. 0 2. 08 0. 0 0.0 0. 0 0. 9 0. 0 0.0 0.0 0.09 0.0 0.0 0.0 0.0 2. 94

Total aromatics 0. 0 2. 34 3. 2 2. 94

Aromatics in Product, vol. percent:

0. 1 2. 3 0. 14 0. 0. 0 0. 1 0. 7 1. 0.0 0. 49 0.0 0. 1 1. 09 0. 0.0 0.45 0. 0 0. 1 0.0 0. 0. 0 0. 0 0. 0 0. Naphthalene 0. 0 0. 0 0. 0 0.

Total aromatics 0.1 2.6 2.87 2.

nCorrected for the monocyclic aromatics added to the feed.

bInsuticient product for analysis. The effects of the aromatichydrocarbons are readily apparent from the foregoing. Upon addition ofbenzene to the feed, the undesired production of light C3-C5 parafnsdecreased from to 17%,-While the desired C-jgasoline fraction remainedconstant at 18%. The -use of mixed xylenes further lowered the lightparain production to 12%, while the 06+ gasoline stayed constant at 18%.In each case, it will be noted that there was a obtained were due to themodified hydrocracking of parafns brought about by the aromatichydrocarbon, and

signicant increase in the -pentane and vhexane iso/ normal were notcaused by the hydrocracking of the aromatics. It Wil-l be noted thatnaphthalene greatly suppressed all hydrocracking.

Results analogous to those indicated in the foregoing example areobtained when other catalysts and conditions, other feedstocks and otherprocess conditions Within the broad purview of the above disclosure areemployed. It is hence not intended lto limit the invention to thedetails of the example or drawing, but only broadly as defined in thefollowing claims:

I claim:

l. A process for obtaining a high-octane gasoline from a predominantlyparaiiin gas oil feedstock boiling above the gasoline range andcontaining monocyclic and polycyclic aromatic hydrocarbons whichcomprises:

(A) separating said feedstock into an essentially aromatic portion andan essentially paraffinic portion;

(B) fractionating said aromatic portion to obtain an overhead fractionboiling between about 400 and 550 F., and a heavier bottoms fractioncontaining poycyclic aromatic hydrocarbons;

(C) subjecting said overhead fraction to hydrodealkylation to convertmethyl naphthaleues to naphthalene and higher alkyl benzenes to loweralkyl benzenes;

(D) fractionating the product from said dealkylation to recovernaphthalene and a monocyclic hydrocarbon overhead;

(E) blending said paraflinic feed portion with said monocyclichydrocarbon Ioverhead fraction;

(F) subjecting the resulting blend of parainic feed Vand monocyclicaromatic hydrocarbons to hydrocracking with added hydrogen in thepresence of a hydrocracking catalyst comprising a Group VIII metalhydrogenating component deposited upon a refractory cracking base, theconditions of hydrocracking including a temperature between about 400and 850 F., a pressure between about 400 and 3,000 p.s.i.g., and aliquid hourly space velocity between about 0.5 and 15, said conditionsbeing further correlated with each other so as to effect a substantialhydrocracking of parafiinic hydrocarbons without substantialhydrogenation of said monocyclic aromatic hydrocarbons, and recoveringfrom said hydrocracking a gasoline fraction comprising monocyclicaromatic hydrocarbons and a paraffinic portion relatively richer inisoparains than would be obtained under the same hydrocrackingconditions in the absence of monocyclic aromatic hydrocarbons.

2. A process as defined in claim 1 wherein said feed separation step (A)is solvent extraction.

3. A process as delined in claim l wherein said paraffinic portioncontains less than about 2% by volume of polycyclic aromatichydrocarbons.

4. A process as defined in claim 1 wherein about 0.5 to 10% by volume ofsaid monocyclic aromatic overhead fraction is blended With said paranicfeed portion, based on the parailnic feed portion.

5. A process for obtaining a high-octane gasoline from a predominantlyparainic gas-oil feedstock boiling above the gasoline range andcontaining at lea-st about 2% by Volume of polycyclie aromatichydrocarbons, which comprlses: l

(A) subjecting said feedstock to a separatory treatment to effect atleast a partial removal of said polycyclic aromatic hydrocarbons andproduce a rainate oil containing less than about 2% by volume ofpolycyclic aromatic hydrocarbons;

(B) blending `said rainate oil with at least about 0.5%

by volume of added monocyclic aromatic hydrocarbon; and (C) subjectingthe resulting blend of parainic and monocyclic aromatic hydrocarbons tohydrocracking n with added hydrogen in the presence of a hydroc crackingcatalyst comprising a Group VIII metal hydrogenating component depositedupon a refractory cracking base, the conditions of hydrocrackingincluding a temperature between about 400-850 F., a pressure betweenabout 400 and 3,000 p.s.i.g., anda liquid hourly space velocity betweenabout 0.5 and 15, lsaid conditions being further correlated with eachother so as to efeot a substantial hydrocracking of parainichydrocarbons without substantial hydrogenation of said monocyclicaromatic hydrocarbons, and recovering from said hydrocracking a gasolinefraction comprising monocyclic aromatic hydrocarbons and a parafiinicportion relatively richer References Cited in the le of this patentUNITED STATES PATENTS Pier et al June 10, 1941 Tongberg Dec. 8, 1942Lanning Feb. 3, 1953 Hetzel Ian. 4, 1955 Doumani Peb. 14, 1956 MertesMar. 5, 1963

5. A PROCESS FOR OBTAINING A HIGH-OCTANE GASOLINE FROM A PREDOMINANTLYPARAFFINIC GAS-OIL FEEDSTOCK BOILING ABOVE THE GASOLINE RANGE ANDCONTAINING AT LEAST ABOUT 2% BY VOLUME OF POLYCYCLIC AROMATICHYDROCARBON, WHICH COMPRISES: (A) SUBJECTING SAID FEEDSTOCK TO ASEPARATORY TREATMENT TO EFFECT AT LEAST A PARTIAL REMOVAL OF SAIDPOLYCYCLIC AROMATIC HYDROCARBONS AND PRODUCE A RAFFINATE OIL CONTAININGLESS THAN ABOUT 2% BY VOLUME OF POLYCYCLIC AROMATIC HYDROCARBONS; (B)BLENDING SAID RAFFINATE OIL WITH AT LEAST ABOUT 0.5% BY VOLUME OF ADDEDNOMOCYCLIC AROMATIC HYDROCARBON; AND (C) SUBJECTING THE RESULTING BLENDOF PARAFFINIC AND MONOCYCLIC AROMATIC HYDROCARBONS TO HYDROCRACKING WITHADDED HYDROGEN IN THE PRESENCE OF A HYDROCRACKING CATALYST CONPRISING AGROUP VIII METAL HYDROGENATING COMPONENET DEPOSITED UPON A REFRACTORYCRACKING BASE, THE CONDITIONS OF HYDROCRACKING INCLUDING A TEMPERATUREBETWEEN ABOUT 400-850* F., A PRESSURE BETWEEN ABOUT 400 AND 3,000P.S.I.G., AND A LIQUID HOURLY SPACE VELOCITY BETWEEN ABOUT 0.5 AND 15,SAID CONDITIONS BEING FURTHER CORRELATED WITH EACH OTHER SO AS TO EFFECTA SUBSTANTIAL HYDROCRACKING OF PARAFFINIC HYDROCARBONS WITHOUTSUBSTANTIAL HYDROGENATION OF SAID MONOCYCLIC AROMATIC HYDROCARBONS, ANDRECOVERING FROM SAID HYDROCRACKING A GASOLINE FRACTION COMPRISINGMONOCYCLIC AROMATIC HYDROCARBONS AND A PARAFFINIC PORTION RELATIVELYRICHER IN ISOPARAFFINS THEN WOULD BE OBTAINED UNDER THE SAMEHYDROCRACKING CONDITIONS IN THE ABSENCE OF SAID ADDED MONOCYCLICAROMATIC HYDROCARBONS.